In high frequency oscillators stray capacitances and lead inductances become very important in determining the oscillation frequency, output power, feedback fraction and other ac quantities. High frequency oscillators heretofore provided have an oscillator circuit board with a resonator or tank circuit in the form of a quarter wave transmission line section printed or etched on the circuit substrate, and a metal cover over the oscillator circuit. The capacitance between the resonator and the cover causes large cover frequency shift effects. The oscillator frequency is frequency modulated by microscopic movements of the cover caused by noise and vibration creating microphonic effects that appear as degraded electrical phase noise performance of the oscillator.